The present invention is related generally to methods for separating components from gas mixtures, and more particularly to an improved method of separating carbon dioxide from a gas mixture using a fluid dynamic instability.
The combustion of fossil fuels produces a stream of flue gas which contains carbon dioxide (CO2) and other components. In order to control atmospheric carbon emissions, various separation technologies will be required to remove the CO2 from the flue gas. However, there is a need to enhance the efficiency of CO2 separation beyond what is currently available commercially. Current flue gas separation technologies include the use of solvents, cryogenic techniques, membranes, and solid sorbents. Each of these technologies can be performed on a large scale, but all are energy intensive when applied to capturing CO2 in dilute streams, such as flue gas, which is approximately 15% by volume for coal combustion, 13% for oil, and 9% for natural gas.
Amine-based solvents are the most energy efficient conventional option for removing CO2 from flue gas. However, energy consumption is inherently high due to the large dilutions with water that are needed to prevent corrosion of equipment and to avoid flow problems caused by viscosity increases for fast-reacting amines, such as monoethanolamine (MEA). In commercial MEA applications, a large volume of solvent (typically containing 70% to 88% water) must be heated to release a relatively small amount of gas and regenerate the solvent. In addition, the overall efficiency of traditional tower stripping designs suffers from mass-transfer rate limitations. Therefore, it would be desirable to provide an improved method of separating components such as carbon dioxide from flue gases or other gas mixtures.
The above objective as well as others not specifically enumerated are achieved by an improved method of separating a component from a gas mixture in accordance with the invention. In a first embodiment, the method is used to separate a non-aqueous component from a gas mixture. The method includes flowing a liquid solvent down a wire so that the solvent forms drops which flow down the wire. The formation and motion of the drops on the wire is caused by a fluid instability of the solvent. The fluid instability usually includes mixing of the content of the drops such that liquid solvent flows from the surface of the drops into the interior of the drops. Typically, the solvent forms drops of different sizes which collide with one another as they flow down the wire, causing mixing of the content of the drops. The gas mixture is flowed into contact with the solvent on the wire so that the solvent absorbs the non-aqueous component from the gas mixture. The fluid instability of the solvent increases the mass transfer rate of the absorption process.
In another embodiment of the method, a liquid solvent is flowed down a wire so that the solvent forms drops which flow down the wire. The flow of the drops down the wire creates fluid instability of the solvent. The solvent is reactive with the gas component. The gas mixture is flowed into contact with the solvent on the wire so that the solvent reacts with and absorbs the gas component. The fluid instability of the solvent increases the rate of reaction of the solvent with the gas component by at least about 50%, compared to the same reaction with the solvent in a fluid stable condition.
In a particular embodiment, the invention relates to a method of separating carbon dioxide from a gas mixture. A liquid solvent is flowed down a wire so that the solvent forms drops which flow down the wire. The flow of the drops down the wire creates fluid instability of the solvent. The solvent is reactive with carbon dioxide. A gas mixture containing carbon dioxide is flowed into contact with the solvent on the wire so that the solvent reacts with and absorbs the carbon dioxide from the gas mixture. The fluid instability of the solvent increases the mass transfer rate of the absorption process.
In another embodiment of the method, a liquid containing a solvent is flowed down a wire so that the liquid forms drops which flow down the wire. The flow of the drops down the wire creates fluid instability of the liquid. The solvent is reactive with the gas component. The liquid further contains an activator which promotes the reaction of the solvent with the gas component. The gas mixture is flowed into contact with the solvent on the wire so that the solvent reacts with and absorbs the component from the gas mixture. The fluid instability of the liquid increases the mass transfer rate of the absorption process.
In a further embodiment of the method, a liquid solvent is flowed down a wire so that the solvent forms drops which flow down the wire. The flow of the drops down the wire creates fluid instability of the solvent. The method includes an additional step of exciting the fluid instability of the solvent. The fluid instability can be excited by passive means, such as by placing obstacles on the wire and passing the flow of solvent over the obstacles. The fluid instability can also be excited by active means, such as by mechanically enhancing the instability by vibrating, twisting or translating the wire. The fluid instability can also be excited by heating the fluid on the wire. The gas mixture is flowed into contact with the solvent on the wire so that the solvent absorbs the component from the gas mixture. The fluid instability of the solvent increases the mass transfer rate of the absorption process.
In another embodiment of the method, the liquid solvent comprises a mixture of amine and water. The amine is selected to have physical properties such that the liquid solvent resists formation of solids and has suitable flow characteristics to flow down the wire sufficient to significantly increase the mass transfer rate.
Another embodiment of the invention is a method of stripping a gaseous component from a liquid solvent containing the component. In the method, a liquid solvent containing a gaseous component is flowed down a wire so that the solvent forms drops which flow down the wire. The flow of the drops down the wire creates fluid instability of the solvent. The liquid solvent is heated on the wire so that the gaseous component is released from the solvent. The fluid instability of the solvent increases the mass transfer rate of the stripping process.